This research is designed to study the effects of over- and undernutrition on thyroid hormone physiology and to separate those effects which are related to the diet from those which are associated with change in body weight or composition. Studies will be performed in normal and obese volunteers, and patients with anorexia nervosa and lipoatrophic diabetes mellitus. Measurement of serum concentrations of total and free thyroxine and triiodothyronine will be correlated with studies of peripheral thyroid metabolism using turnover rate techniques and thermogenesis using indirect colorimetry as well as the pituitary response to thyroid releasing hormone. The yearly alterations in weight and thyroid activity of the woodchuck will be studied using similar techniques.